1.Pin A pin against the king, called absolute because the pinned piece cannot legally move as it would expose the king to check. See relative pin.

2. Adjust or j'adoube(Touch-move rule) To adjust the position of a piece on its square without being required to move it. Adjustment can only be done when it is the player's move and the adjustment is preceded by saying "I adjust" or "j'adoube".

3. Advanced pawnA pawn that is on the opponent's side of the board (the fifth rank or higher). An advanced pawn may be weak if it is overextended, lacking support and difficult to defend, or strong if it cramps the enemy by limiting mobility. An advanced passed pawn that threatens to promote can be especially strong.

4. Alekhine's gunA formation in which a queen backs up two rooks on the same file.

5. Anti-SicilianAn opening variation that White uses against the Sicilian Defense (1.e4 c5) other than the most common plan of 2.Nf3 followed by 3.d4 cxd4 4.Nxd4 (the Open Sicilian).

6. AttractionIf a player sacrifices minor or major pieces to expose the enemy king. For example, if the black king has castled and is on the g8-square, white may attempt to "attract" the king by using forcing moves such as Bxh7+, followed by Ng5+ etc. 7. Back-rank mate A checkmate delivered by a rook or queen along a back rank in which the mated king is unable to move up the board because the king is blocked by friendly pieces (usually pawns) on the second rank. This is also sometimes referred to as a back-row mate.

8. Backward pawnA pawn that is behind the pawns of the same color on the adjacent files and that cannot be advanced with the support of another pawn.

9. Bishop pairIn open positions, two bishops (on opposite colors) are considered to have an advantage over two knights or a knight and a bishop. (In closed positions knights may be more valuable than bishops.) The player with two bishops is said to have the bishop pair.

10. Blindfold chess A form of chess in which one or both players are not allowed to see the board.

11. Blitz chess A fast form of chess (Blitz being German for lightning) with a very short time limit, usually 3 or 5 minutes per player for the entire game. With the advent of electronic chess clocks, it is often the case that the time remaining is incremented by 1 or 2 seconds per move.

16. Bustan opening, A famous example is Bobby Fischer's 1961 article "A Bust to the King's Gambit" in which he wrote, "In my opinion, the King's Gambit is busted.

17. Bye A tournament round in which a player does not have a game, usually because there are an odd number of players. A bye is normally scored as a win (1 point), although in some tournaments a player is permitted to choose to take a bye (usually in the first or last round) and score it as a draw (½ point).